4N.I.In the case of any factory constructed or converted for use as a factory before the coming into operation of section 35 of the Factories Act (Northern Ireland) 1938 [1938 c.23] (that is to say the 1st July 1939) which is not a factory to which paragraph 3 of this Schedule applies, no offence shall be deemed to be committed under section 41 of this Act by reason of the use of the factory during any period that may elapse before the grant or refusal of a certificate under that section by the fire authority, and if the fire authority refuse to grant a certificate in respect of the factory unless alterations are made, no such offence shall be deemed to be committed while the alterations are being carried out in accordance with the requirements of the authority.